Code or regulations that have been enacted for elevator systems may require the elevator system to drop or engage a brake at least once in the time period between an elevator car stopping at a first landing or floor and then leaving that first landing/floor for a second landing/floor. The code/regulations may also require the elevator system to de-energize at least a portion of the propulsion system (e.g., drive or motor) during that time period.
In conventional elevator systems, as an elevator car approaches a destination landing or floor, the elevator car decelerates. When the elevator car reaches a condition of near zero velocity with the car sufficiently close to the desired floor landing the brake is dropped. Then, as the doors open and the load in the elevator car changes (e.g., as passengers in the elevator car exit the elevator car), if the elevator car moves away from the sill level in an amount greater than a threshold (e.g., 0.5 inches), the elevator system is required to perform a re-leveling operation to bring the elevator car back to the landing within the threshold. To perform the re-leveling operation, the elevator system may check a safety chain as part of a pre-flight check, pre-torque the motor, lift the brake, and then follow a motion profile to correct the elevator car's position.
The elevator system may initiate a re-leveling operation multiple times at a landing based on the changes or transfer of load at the landing (e.g., exit or entry of passengers or freight). The timing of the power cycling and brake drop-and-lift is critical, especially when the hoisting components are very compliant, such as in high-rise systems or buildings. For example, if the brake cycling happens shortly after arrival at a destination landing, fast load transfer leads to an excessive amount of movement, representing a risk. On the other hand, if the brake cycling is delayed until just before the elevator car is ready to depart from a landing, it adds to the start delay for a given run, representing a user or passenger nuisance. This invention describes a control system concept which can optimize the re-leveling and brake control operation.
Re-leveling may need to be performed in high-rise systems or buildings more frequently relative to smaller buildings or structures due to longer ropes/cables used in the high-rise buildings having greater elasticity (and hence, being more susceptible to elevator car movement in response to load transfer). Elevator systems and infrastructure are tending to increase in size or capacity (e.g., stacked elevator cars) to accommodate more passengers or load, which leads to a potential increase in load transfer dynamics/changes. Re-leveling operations are not instantaneous, but incur delay due the need to verify proper operation of safety circuits and change the state of the brake (e.g., lift the brake) and the state of the machine or motor (e.g., energize/pre-torque the machine or motor).